This invention relates generally to cellular telecommunication systems and, more particularly, to systems for generating statistical usage and billing information in cellular telecommunication networks that employ earth-orbiting satellites.
Satellite-based cellular telephone systems have been proposed in recent years, to provide worldwide telecommunication coverage. These systems are similar to terrestrial cellular telecommunication systems in that they have a grid of service zones or cells. They differ in that the satellite systems use a constellation of satellites with communication transponders instead of fixed radio towers as in terrestrial cellular systems. In a satellite-based cellular system, a user located in one of the cells communicates with the system through the satellite transponder covering a service zone in which the user is located. The satellite then communicates either with another satellite or with an earth station, to forward the call to a receiving party, who may be another satellite cellular user or a user connected through a conventional public switched telephone network (PSTN). Since a satellite-based cellular system provides worldwide communications, its users may be interconnected through an extensive and changing set of network elements. A users call could start through one satellite and an associated earth station, and be handed over to one or more other satellites and earth stations during the course of the call. Also, many of the calls use not only the resources of the satellite system, but the resources of other telephone communication providers as well.
Keeping track of how all the system resources are allocated and used in each call is necessary for billing purposes and for other reasons, such as statistics gathering for use in system design and expansion, traffic analysis and reporting, or detection and prevention of fraud. The present invention is concerned with generating system usage data for billing purposes. Gathering usage data in a conventional terrestrial cellular telephone system makes use of a call data record (CDR) that is generated for each call initiated by a user of the system. So long as the user remains in the service area of his cellular service provider, generating the billing data is a relatively simple process because the user is typically billed at a flat per-minute rate for use of the cellular system. If the user connects with a conventional telephone in a public switched telephone network (PSTN), additional charges may be incurred, including long-distance charges, depending on the location of the called telephone. If the cellular user is outside his normal service area, additional charges are usually involved, for "roaming" into another service area, but the billing statistics are still relatively simple to gather, sort and distribute.
In a satellite-based telecommunications system, a single call may use resources of multiple satellites, earth stations, radio-frequency communication links, public switched telephone networks and other network elements. Moreover, the times that these resources are used and the billing rates that apply to them may not be readily available at the time the call is made, and resources used may change during the call. A further difficulty is that, even if resource usage information is transmitted to a central site as soon as it becomes available, the information will not necessarily arrive at the same time. Consequently, gathering and sorting resource usage data becomes an extremely difficult task when a cellular system includes multiple communication satellites and associated resources scattered around the world. Another billing difficulty arises because users will typically purchase access to the system from a service provider in a particular country, but may operate a user terminal in practically any country. From the user's standpoint, connection from the user terminal to any telephone in the world must be automatic and "seamless." Yet the resource usage records must be automatically associated with every call, attributed to the user who made the call, and distributed automatically to the user's service provider for billing. It will be apparent that there is a need for a telecommunication billing system that meets all these requirements. The present invention satisfies this need.